This invention is directed to a process and apparatus for removing chemical contaminants from groundwater. More particularly, the present invention is directed to a process and apparatus in which vacuum extraction is used to remove soil contaminants in both the saturated and vadose zones. One embodiment of the present invention is directed to a process for removing contaminants from a contaminated area of the ground having a vadose zone and a water table, which comprises providing a borehole in the contaminated area to a depth below the water table; placing in the borehole to a depth below the water table a perforated riser pipe inside of which is situated a vacuum extraction pipe with a bottom opening situated within the perforated riser pipe, said vacuum extraction pipe containing groundwater prior to application of a vacuum thereto, said vacuum extraction pipe having at least one gas inlet situated below the groundwater level in the vacuum extraction pipe; while introducing a gas into the riser pipe, applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a two-phase common stream; introducing a gas into the vacuum extraction pipe at a level below the groundwater level in the vacuum extraction pipe to initiate two-phase flow within the vacuum extraction pipe; forming from the common stream a stream which is primarily liquid and a stream which, is primarily gaseous; and separately treating the separated liquid and gas streams. Another embodiment of the present invention is directed to an apparatus for removing contaminants from a contaminated area of the ground having a water table and a vadose zone above the water table which comprises a perforated riser pipe extending downwardly from the surface of the ground to a level below the water table, a vacuum extraction pipe situated inside of the riser pipe and having a bottom opening situated within the perforated riser pipe, said vacuum extraction pipe containing groundwater prior to application of a vacuum thereto, said vacuum extraction pipe having at least one gas inlet situated below the groundwater level in the vacuum extraction pipe for introducing a gas into the vacuum extraction pipe to initiate two-phase flow within the vacuum extraction pipe, a riser pipe gas inlet for introducing a gas into the riser pipe, a vacuum-forming apparatus in fluid communication with the vacuum extraction pipe and adapted to form a zone of reduced pressure in the ground around the riser pipe, whereby gases and liquid can be drawn from the ground into the riser pipe and from the riser pipe into the vacuum extraction pipe and conveyed to the surface as a two-phase common stream, and a means for receiving the common stream and separating the stream into separate gas and liquid streams.
Contaminants can exist in subsurface soil and groundwater in the liquid or vapor phase as discrete substances and mixed with and/or dissolved in groundwater and soil gases. Various contaminants can be found in groundwater and soil, such as volatile compounds, including volatile organic compounds, nonvolatile materials, metal contaminants, and the like. Such contaminants can be found and dealt with in the vadose (unsaturated) zone found between the surface of the earth and the water table, at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
At many industrial and commercial facilities and at waste handling and disposal sites, soil and groundwater are contaminated with suspended or water-soluble chemicals, or both. A variety of techniques have been used for removal of contaminants and remediation of affected soil. One common technique entails the excavation and off-site treatment of the soil. Another technique entails saturating the contaminated soil with water in situ, causing the contaminants to be leached slowly from the soil by the water. The contaminated water can then be removed.
Techniques have also been proposed for removing volatile organic contaminants from soil by vacuum extraction. For example, in U.S. Pat. No. 4,323,122, it was proposed that a vacuum be applied in a borehole at the level of the water table, the assumption being that a contaminant such as gasoline, which is lighter than water, would float on the water table and present a layer that could be drawn off by vacuum applied to the liquid at or around that level. U.S. Pat. No. 4,323,122 (Knopik) discloses a system and method for recovering organic liquid such as gasoline which has settled on the water table in underground areas. The system comprises a conduit extending from the ground surface to a point just above the water table, a collection head fitted on the lower end of the conduit, a collection vessel connected to the upper end of the conduit, and an exhaust means for creating less than atmospheric pressure in the vessel. The collection head has a liquid impermeable end portion and a liquid permeable intermediate portion for permitting the passage of liquid. The process comprises providing an opening in the ground to a point beneath the surface of the water table, positioning the conduit with the collection head in place so that the liquid permeable wall of the collection head is just above the surface of the water table, connecting the conduit to the collection vessel intake, and exhausting air and other gaseous materials from the vessel to cause liquid to flow into the collection head through the conduit into the vessel.
Others have suggested the possibility of venting soil above the water table (i.e., in the vadose zone) to cause vaporization of the contaminant in the soil, and then drawing off the contaminant in the vapor phase. Groundwater requiring treatment is in such processes conventionally removed by pumping from separate conventional water wells. In situations in which water does flow into vacuum extraction wells, it has been suggested that a second, liquid phase pump be placed either in the well or at the surface to remove the water through a second conduit. For example, U.S. Pat. No. 4,660,639 (Visser et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for the removal of volatile contaminants from the vadose zone of contaminated ground by extracting volatilized contaminants from the vadose zone by way of one or more vacuum extraction wells. The process entails drilling one or more wells into the subsurface media in the contaminated area, the well being constructed so that fluids in the vadose zone can flow into the well, whereas the liquid in the saturated zone below the water table cannot substantially flow into the well. The borehole and conduit of the well can optionally extend below the water table, in which case the vacuum applied to the upper portion of the conduit will be effective to draw contaminant from the vadose zone, but insufficient to draw a significant amount of water from the saturated zone into the conduit. If it is desired to remove groundwater from below the water table, this removal is accomplished either by a separate sampling device situated in the borehole or through a separate well.
In addition, Stinson, "EPA Site Demonstration of the Terra Vac In Situ Vacuum Extraction Process in Groveland, Mass.", Air & Waste Management Association, Vol. 39, No. 8, pages 1054 to 1062 (1989), the disclosure of which is totally incorporated herein by reference, discloses an evaluation of an in situ vacuum extraction process. The process entails removal of contaminants from the vadose zone by vacuum. Wells are installed in the contaminated vadose soil. A vacuum pump or blower induces air flow through the soil, stripping and volatilizing volatile organic compounds from the soil matrix into the air stream. Liquid water, if present in the soil, is also extracted along with the contamination. The two-phase stream of contaminated air and water flows to a vapor/liquid separator where contaminated water is removed. The contaminated air stream then flows through a treatment system such as gas-phase activated carbon to remove contaminants from the air stream. The clean air is exhausted to the atmosphere through a vent. U.S. Pat. No. 4,593,760 (Visser et al.), the disclosure of which is totally incorporated herein by reference, and U.S. Pat. No. Re. 33,102, the disclosure of which is totally incorporated herein by reference, also disclose processes for removal of volatile contaminants from the vadose zone of contaminated ground by pumping volatilized contaminants from the vadose zone using one or more vacuum extraction wells.
"Forced Venting to Remove Gasoline Vapor from a Large-Scale Model Aquifer," American Petroleum Institute, Health and Environmental Sciences Department, API Publication No. 4431 (1984) discloses the results of experiments examining forced venting of air through the soil above a gasoline spill in a model aquifer. Various flow rates and geometries for the venting plumbing were used to determine the most efficient method of removing gasoline from the underground environment and lowering gasoline vapor concentrations in the unsaturated zone above the spill.
"Venting for the Removal of Hydrocarbon Vapors from Gasoline Contaminated Soil," J. Thornton and W. Wootan, J. Environ. Sci. Health, A 17(1), 31-44 (1982) discloses the results of an experiment investigating the use of a venting strategy to remove gasoline vapors from contaminated soil strata. A contained gasoline leak was created in a large outdoor facility which simulates soil strata and a static water table. An air flow was established, and vapor samples taken before, during, and after venting were checked for hydrocarbon content.
U.S. Pat. No. 4,892,664 (Miller), the disclosure of which is totally incorporated herein by reference, discloses a method and system for decontaminating water, such as groundwater or process effluent, which is contaminated by small concentrations of dissolved volatile organic compounds. The process includes introducing a flow of the water to an air stripping stage in which the water is directed through the column to air strip organic molecules from the contaminated water, releasing the decontaminated water to the environment, pretreating the organic compounds carrying air in the substantial absence of water through a preheater, passing the heated air through a catalytic stage that oxidizes the organic compounds, and releasing the gaseous effluent from the catalytic stage to the atmosphere. Water containing small concentrations of dissolved volatile organic compounds can also be decontaminated by including an apparatus for retrofitting an existing air stripper for this purpose.
Further, U.S. Pat. No. 4,444,260 (Boyd et al.) discloses a method for the treatment of oil well production streams to process oil-contaminated sand to recover oil therefrom and produce an ecologically acceptable clean sand residue. The process entails separating the production fluid from an oil well having sand entrained therein from a plurality of components, one of which comprises an oil-contaminated sand. The contaminated sand is contacted with a light oil solvent to initiate a solvating action of the oil contaminant. The resulting mixture of oil-contaminated sand and solvent is then contacted with water and the system then gravity separated into discrete sand, water, and oil phases. The oil and water phases can be removed from the sand and the sand phase again contacted with water and the resulting mixture is then subjected to gravity separation to produce separate sand and water phases. The water phase is then removed and the sand passed to a suitable disposal facility.
Additionally, U.S. Pat. No. 4,730,672 (Payne) and U.S. Pat. No. 4,890,673 (Payne), the disclosures of each of which are totally incorporated herein by reference, disclose a method and apparatus for collecting volatile contaminants from the vadose layer of earth. The apparatus is a closed-loop device which includes one or more contaminant withdrawal wells surrounded by multiple air reinjection wells connected by a conduit. One or more pumps serve to draw volatilized contaminant through the withdrawal well to the connecting conduit where it is captured or neutralized. Residual air from the withdrawal well is urged back into the ground through the air reinjection wells to encourage further contaminant to move toward the withdrawal well for collection.
U.S. Pat. No. 4,945,988 (Payne et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for removing and disposing of or neutralizing volatile contaminants existing, in the vadose zone of earth and also in a below ground aquifer. The process includes the injection of substantially oxygen free air into the aquifer to retard the formation of aerobic bacteria and injection of oxygen rich air into the vadose zone to stimulate bacterial growth which aids contaminant recovery. Volatilized contaminants are pulled out of the soil through withdrawal wells which terminate in the vadose zone.
U.S. Pat. No. 4,886,119 (Bernhardt et al.) discloses a process for driving volatile impurities from a ground by means of air by aspirating an afterflow air and impurities containing gases which penetrated through a permeable wall of a shaft in a ground, at one or several locations. In regions of expected high gas contents, air afterflow passages are extended to these regions for supplying the afterflow air, and an adjustable afterflow resistance is arranged in the passages for influencing a negative pressure value and a flow speed in these regions.
U.S. Pat. No. 3,743,355 (Blackwell et al.) discloses a method for withdrawing hazardous gases from a water saturated subterranean formation containing a mineral deposit suitable for mining. The process entails drilling wells through the subterranean formation and withdrawing water from the subterranean formation to establish permeability to gas within the subterranean formation. Gas is then withdrawn from the formation by means of the wells. The method is particularly applicable for reducing the influx of radon into a mine contained in a mineral deposit.
U.S. Pat. No. 5,050,676 (Hess et al.) and U.S. Pat. No. 5,197,541 (Hess et al.), the disclosures of each of which are totally incorporated herein by reference, disclose an apparatus and process for extracting contaminants from soil both above and below the water table. The process comprises placing a perforated riser pipe in a borehole in a selected portion of the contaminated area, wherein the perforations of the riser pipe are situated below the water table. Optionally, some of the perforations in the riser pipe can also be situated in the vadose zone above the water table. A vacuum is then applied to the pipe to draw gases and liquids from the soil into the pipe and to transport the gases and liquids to the surface as a common stream. At the surface, the common stream is separated into a primarily liquid stream and a primarily gaseous stream, and the separated streams are then treated separately.
U.S. Pat. No. 5,172,764 (Hajali et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for removing contaminants from a contaminated area of the ground having a vadose zone and a water table which comprises providing a borehole in the contaminated area; placing in the borehole a perforated riser pipe inside of which is situated a vacuum extraction pipe with an opening situated near, at, or at any point below the water table within the perforated riser pipe, while introducing a gas into the riser pipe, applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a common stream; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and separately treating the separated liquid and gas streams. Also disclosed is an apparatus for carrying out the process.
U.S. Pat. No. 5,076,360 (Morrow), the disclosure of which is totally incorporated herein by reference, discloses a method and apparatus for vacuum extraction of contaminants from the ground which, in a preferred embodiment, involves vacuum withdrawal of liquid and gaseous phases as a common stream, separation of the liquid and gaseous phases, and subsequent treatment of the separated liquid and gases to produce clean effluent. A primed vacuum extraction employs a single vacuum generating device to remove contaminants in both the liquid stream and soil gases through a single well casing utilizing a priming tube which introduces air or other gas to the liquid collected at the bottom of a well, permitting vacuum extraction of both liquids and gases from the subsurface by way of wells having a liquid layer which is more than thirty feet below the soil surface or in which a screened interval of the extraction pipe is entirely below the liquid surface.
U.S. Pat. No. 1,547,194 (Arbon) discloses a system for elevating oil consisting in packing a well between the eduction tube and casing to cause the accumulation of the gas, arranging valved ejectors in said tube above and below the packing, and regulating the valves to cause successive elevation of fluid in the tube.
U.S. Pat. No. 753,045 (Cooper) discloses a method of obtaining gas from wells containing water with gas held in solution which consists in lifting the water in the well by means of a hydrocarbon gas introduced under pressure into the water column below and collecting the gas liberated from the lifted water.
U.S. Pat. No. 1,291,130 (Purchas) discloses an eduction pipe for air lifts, the cross section of which varies in steps, the maximum cross section being at the bottom and adapted to be submerged, the minimum cross section following the maximum cross section, the section larger than the minimum but smaller than the maximum following the minimum section.
U.S. Pat. No. 2,026,419 (Davidson) discloses an apparatus and process for enlarging the normal subterranean liquid capacity of the supply area of a tube well which consists of oscillating indigenous liquid of the area by pumping forces set up in the tube to dislodge alluvium and simultaneously applying air pressure to remove the alluvium from the well.
U.S. Pat. No. 4,017,120 (Carlson et al.) discloses the production of hot brines containing dissolved gases from liquid dominated geothermal wells by utilizing lift gases of essentially the same composition as the dissolved gases. The lift gas is separated from the produced brine and recycled. Heat is abstracted from the separated brine, which may be returned to the aquifer, processed for its mineral content, or discarded. The gas lift is carried out under temperature and pressure conditions such that the precipitation of minerals from the brine does not occur in the well bore.
U.S. Pat. No. 4,180,980 (Marks et al.) discloses a method and apparatus for releasing for use air that has been absorbed under pressure in sea water or in any other large free body of water. An elongated conduit or other equivalent means is vertically disposed so that air released from its upper end is collected by an open bottom container serving is a reservoir. The interface of the collected air and the submersion level of water within the reservoir is substantially below the free water surface level. A small amount of gas is introduced at the lower end of the conduit so as to rise upwardly through the conduit, thereby carrying water behind it, and to initiate a continuous process in which the rising water is under decreasing pressure, at times increasing temperature, thereby releasing more air, which in turn carries more water behind it. Air from the reservoir can be used as an energy source.
U.S. Pat. No. 4,267,885 (Sanderford) discloses a method and apparatus to optimize and control the production of an oil well which is being artificially produced by gas-lift techniques. The invention is suitable for use with either continuous or intermittent gas-lift operation and can be used with a combination of both. The temperature of the fluid at the wellhead is sensed and used to determine the injection parameter values to optimize well production. In one embodiment, a process control unit is programmed according to the inventive method to interpret the temperature data and to control the gas control valve to optimize production.
U.S. Pat. No. 4,895,085 (Chips) discloses a method and structure whereby contaminated soil is decontaminated in situ by the extraction of vapor from the soil and subsequent destruction of the contaminants contained in the interstitial fluid of the soil by processing the fluid through an internal combustion engine or other suitable combustion means. To achieve this purpose, a means of conducting the fluid from the soil to a manifold system is provided.
U.S. Pat. No. 4,982,788 (Donnelly) discloses an apparatus and method for removing hazardous volatile contaminants from the ground by circulating air between two substantially parallel wells and by removing the vapors of the organic compound from the circulated air using at least one of a condenser and a demister. To enhance efficiency the air is recirculated in a closed loop. The heat output of the condensation process is used to heat the recirculated air. Pipes having openings along only a limited portion of their lengths are placed in the wells and the depth of the openings adjusted to treat one level at a time, thereby preventing shunting of air through more porous soil layers. Flow rates can be equalized by using circumferentially placed induction wells surrounding an extraction well (or the reverse) and by controlling air flow through individual sections of a given level.
U.S. Pat. No. 5,009,266 (Dieter) discloses a method for the in situ removal of mobilizable contaminants, including volatile and semi-volatile organic compounds, from a contaminated unsaturated zone of primarily porous layers of soil. The method comprises pulsatilely injecting heated pressurized steam into a first location in the zone to heat the soil in the zone, and withdrawing the contaminants under subatmospheric pressure from the soil at a second location in the zone. In specific application, the pulsatile injection of steam is used to heat the soil without directly recovering injected steam for a significant period of time until the targeted soil in the zone is uniformly heated to steam temperature. The pulsatile injection directs the heat in particular directions and to particular areas in the soil zone as desired.
U.S. Pat. No. 5,018,576 (Udell et al.) discloses a method for in situ decontamination of contaminated subsurface area by injection of steam into injection wells and withdrawing liquids and vapors from extraction wells under subatmospheric pressure whereby steam is passed through the contaminated area in an essentially horizontal direction. After a substantial portion of the contamination has been removed in this manner, the injection of steam is ceased, but the extraction at subatmospheric pressure is continued, to volatilize and remove the residual water and contaminants trapped in the pores of the soil. The steam injection may be periodically resumed to reheat the area and to replenish the water in the pores.
Although known apparatuses and processes are suitable for their intended purposes, a need remains for a process and apparatus for removing contaminants from groundwater and soil which enables contaminant removal from below and/or above the water table. A need also remains for a process and apparatus for removing contaminants from groundwater and soil which enables contaminant removal from soils of varying air permeability and varying porosity. Further there is a need for a process and apparatus for removing contaminants from groundwater and soil which enables increased flexibility in the location of extraction wells. There is also a need for a process and apparatus for removing contaminants from groundwater and soil that can be implemented by modifying existing vacuum extraction systems. In addition, there is a need for a process and apparatus for removing contaminants from groundwater and soil that enables extraction of contaminants both from the vadose zone and from below the water table through an extraction well having a riser pipe with perforations both above and below the water table. Further, a need exists for a process and apparatus for removing contaminants from groundwater and soil that enables vacuum extraction of contaminants through a well from below the water table when the water table is deeper than the equivalent lift of the vacuum pump connected to the well. There is also a need for a process and apparatus for removing contaminants from groundwater and soil with simplified equipment in that a single vacuum pump can be employed to remove contaminants in both the vapor and liquid phases through a single well or pipe. Additionally, there is a need for a process and apparatus for removing contaminants from groundwater and soil that enables reduction of contaminant concentrations in the extracted groundwater as a result of the mixing of air and water in the vacuum extraction pipe, leading to reduced subsequent water treatment requirements. In addition, there is a need for a process and apparatus for removing contaminants from groundwater and soil that dewaters the saturated zone (groundwater)in the vicinity of the extraction well in some soil conditions, thereby allowing air flow to move through the dewatered soil, which accelerates the extraction rate of contaminants and results in reduced cleanup time. Further, there is a need for a process and apparatus for removing various kinds of contaminants from groundwater and soil, including volatile materials, nonvolatile materials, metal contaminants, and the like.
In addition, it is desirable in a two-phase vacuum extraction system that the flow of both liquid and gas through the well extraction tube be maintained at an adequate velocity of liquid and gas to maximize depression of the water table and accelerate the removal of contaminated groundwater and contaminated soil gas from both the vadose zone and the saturated zone below the water table. When a vacuum extraction pipe is first inserted into a riser pipe, however, the groundwater in the well fills the extraction pipe to the surrounding groundwater level. Subsequently, when a vacuum is applied to the vacuum extraction pipe to initiate the two-phase vacuum extraction process, removal of the groundwater through the vacuum extraction pipe may be difficult or impossible, depending on the length of the extraction pipe situated below the water table. In some instances, it may be necessary to apply extremely high vacuum levels (up to 30 inches of mercury, for example) and/or to manipulate several valves and/or partially or totally withdraw and slowly reinsert the vacuum extraction tube to initiate the two-phase extraction process. Thereafter, when the extraction process is terminated and subsequently restarted in the same well, the recharging of the well with groundwater may lead to the same difficulties encountered at the start-up of the process. Accordingly, a need remains for a method and apparatus for initiating two-phase vacuum extraction of groundwater and soil contaminants which eliminates the need for inconvenient and time-consuming start-up adjustments. There is also a need for a method and apparatus for initiating two-phase vacuum extraction of groundwater and soil contaminants which eliminates the need for moving or removing the vacuum extraction pipe within the riser pipe.
Further, in some instances it may be desirable to remove contaminants from groundwater and soil gases from significant depths, such as thirty feet or greater, and/or to lift the two-phase stream extracted from the well to significant heights, such as in systems wherein the two-phase stream must be lifted over one or more buildings or through ceiling pipes in buildings to reach the separation and treatment location. Accordingly, a need remains for a method and apparatus for initiating two-phase vacuum extraction of groundwater and soil contaminants which enables the extraction from soil of liquids and gases containing contaminants from significant depths. A need also remains for a method and apparatus for initiating two-phase vacuum extraction of groundwater and soil contaminants which enables the conveyance of a two-phase stream of liquids and gases containing soil contaminants to significant heights.